We propose to study the role of pituitary follicle stimulating hormone (FSH) in the regulation of testicular function in rats. Since the first event in a hormone-target cell interaction is binding of the hormone to specific cellular binding sites, we plan to "map" FSH binding sites in testis by localizing the hormone with immunocytochemical and autoradiographic techniques at both light and electron microscopic levels. FSH binding sites will also be characterized in vitro in subcellular fractions of testicular tissue, prepared by differential centrifugation. The distribution, specificity, and saturability of the binding sites will be studied, and their quantity under various experimental conditions will be determined. In order to link FSH binding to functional responses, we shall investigate by both morphological and biochemical criteria the mechanisms whereby FSH stimulates protein synthesis in testis. FSH-induced incorporation of labeled amino acids into proteins will be used to trace subcellular events during protein synthesis and release by electron microscopic autoradiography. These studies will be aimed at clarifying the role of subcellular components of Sertoli cells, known target cells for FSH, in the FSH-induced protein synthesis. Emphasis will be placed on a functionally important FSH-dependent product of the Sertoli cells, androgen binding protein (ABP). ABP will be identified by electrophoresis and immunoprecipitation techniques in gels. Specific antibodies to ABP will also be used for immunocytochemical localization of ABP in testis and epididymis. Finally, attempts will be made to clarify the modulating effects of androgens on testicular events known to be regulated by FSH, and the hormonal regulation of testicular FSH binding sites will be studied. The proposed research will provide a more precise understanding of the regulation of testicular function, and the results may contribute to the development of improved methods for the control of male fertility.